Ocean surface wave measurements using a small autonomous underwater vehicle

Abstract

Small Autonomous Underwater Vehicle (AUV) capabilities are advancing rapidly and small AUV's are being used increasingly to collect many types of oceanographic data. Techniques have been developed, tested by wave simulations, and preliminarily field tested to provide ocean surface wave information, including directional wave spectra, using small AUV's. The techniques are adaptable to several small AUV's being developed and operated by the U.S. Navy. Either one or two small pressure sensors attached to an AUV's hull are utilized. Using two sensors along an AUV's bow-stern axis constitutes a moving slope array for one of the data analysis methods. After corrections for wave-induced vehicle motions measured by small accelerometers and angular rate sensors, three different data processing methods can provide wave information. The first method provides key wave height, period, and direction parameters. The second method treats the corrected wave data as a moving slope array. Both of these methods correct for Doppler shifts caused by an AUV's velocity while it maintains a nearly constant depth. The third method treats the wave motion-corrected wave data as an array of many point measurements made by non-stationary wave sensors with their horizontal positions known as functions of time. Doppler shifts do not occur due to this method's mathematical formulation. The required sensors and a data acquisition/processing system have been integrated into a small AUV used as a test vehicle and the system is being used to collect preliminary field data. The small AUV wave measurement system can be used for coastal wave mapping to support military operations, coastal processes studies, and driving nearshore models such as surf models and sediment transport models.